In the plastics industries it is usual to use processes such as injection molding, extrusion and the like wherein a plastic material is fed into a mold, extruder or other equipment, is heated to soften the material, and pressed, drawn or forced into a desired shape. The plastic material employed in such processing is usually in the form of relatively small particles such as pellets or the like, or frequently in the form of reclaimed or reused plastic which has been obtained from a previous operation.
One of the problems confronting the industry is that the plastic material usually is moist with water, and this moisture interferes with uniformity of operating conditions or performance. At the present time the usual means of overcoming this problem is to heat the plastic material in a drying device, and then on demand take a quantity of the plastic and feed it to the plastic processing equipment. In most cases, and particularly where a number of molds or extruders operate on essentially the same type of plastic material, it is usually the custom to have a single relatively large drier or storage bin of dry plastic centrally located so that a charge of this plastic material can conveniently be placed in the hopper of any other of the various molds or extruders.
The central location of dryers or storage bins for plastic materials has a number of disadvantages. In the first place, when a charge of plastic material is carried across the shop it tends to pick a certain amount of moisture, particularly on a humid day. In the second place a centrally located dryer or bin is at best awkward when two different types of plastic are being used in two different plastic processing equipment. Furthermore, the centrally located operating dryer has, until now, heated appeared to have specific advantages in that a relatively large device economically justifies sophisticated control systems to assure a constant supply of material in constantly good condition.
When attempts have been made to use individual dryers near each mold or extruder the results have been unsatisfactory. At best, such individual dryers have been awkward and inconvenient, have not properly dried the product, or have created virtually as many problems as they have solved.
The solution to these problems has not been apparent, and at the present time such a centrally located dryer or bin is the normal operating procedure in most plastic plants.